Method of improving the surface activity of electrically conductive carrier strips

ABSTRACT

A method of improving the surface activity of electrically conductive carrier strips, to enhance their bonding properties. The surface of the strip is subjected to a high frequency and high gradient alternating electrical field formed between two electrodes. The carrier strip which forms one electrode is conducted over and in direct contact with a roller electrode which forms the other electrode and the surface of which comprises a solid dielectric material. The difficulties which occur when an air gap is present between the strip and the electrode are thereby avoided.

United States Patent n91 Bille Jan. 2, 1973 [54] METHOD OF IMPROVING THE 7 SURFACE ACTIVITY OF 1 ELECTRICALLY CONDUCTIVE CARRIER STRIPS [75] Inventor: Holger Steen Bille, Hamfelde, Germany [73] Assignee: Softal Elektronik G.m.b.H., Hamburg, Germany 22 Filed: Feb. 25,1971

[21] Appl.No.: 118,832

[30] Foreign Application Priority Data March 26, 1970 Germany ..P 20 14 646.7

[52] US. Cl. ..3l7/262 A [51] Int. Cl. ..H01l 19/00 [58] Field of Search ..3l7/262 A [56] References Cited UNITED STATES PATENTS 3,483,374 12/1969 Erben ..31"7/262A OTHER PUBLICATIONS Guide to Corona Film Treating May 1961 Article in Plastics Engineering by l-leide et al. pp 199-206.

Primary Examiner-J. D. Miller Assistant Examiner-Harry E. Moose, Jr. Attorney-Williamson, Palmatier & Bains [5 7 ABSTRACT A method of improving the surface activity of electrically conductive carrier strips, to enhance their bonding properties. The surface of the strip is subjected to a high frequency and high gradient alternating electrical field formed between two electrodes. The carrier strip which forms one electrode is conducted over and in direct contact with a roller electrode which forms the other electrode and the surface of which comprises a solid dielectric material. The difficulties which occur when an air gap is present between the strip and the electrode are thereby avoided.

5 Claims, 1 Drawing Figure Pmmmm 21375 3.708.733

k/jimmy f METHOD OF IMPROVING THE SURFACE ACTIVITY OF ELECTRICALLY CONDUCTIVE CARRIER STRIPS The present invention relates to methods for improving the surface activity of electrically conductive carrier strips, such as aluminum foils.

Before electrically conductive carrier strips, in particular metal foils can be printed on, varnished, coated and lined, they must be subjected to a preliminary treatment and degreased, in order to increase their adhering capability. A surface activation must take place which ensures that printing inks, coloring materials are accepted and are sufficiently securely joined to the metal foil.

In a known process of the type mentioned above, the electrically conductive carrier strips which is to be activated, and which forms an electrode, is generally conducted over electrically neutral and insulated transport or guiding rollers. A driven rotating roller electrode which forms an opposite electrode to the carrier strip is arranged in the region of at least one of these guiding rollers, at a distance from the carrier strip to be treated. Thus, there always exists a gap between the two electrodes, i.e. between the electrically conductive carrier strip and the rotating roller electrode, which electrode is in fact usually coated with a dielectric material. Thus at least two rollers, one transportor guiding roller and one roller electrode are required for the execution of this known process. Further, the gap between these two rollers must be set at an appropriate value, and to insert the carrier strip, it must be threaded carefully between the rollers. This operation can be decidedly difficult in the case of carrier strip activation apparatus having poor accessibility. As the gap has a relatively high impedance, a correspondingly high degree of electrical energy must be applied in order to overcome this impedance, for the full activation of the selected surface. It has become known, in order to increase its surface activity, to subject anon-conductive synthetic plastics material foil to a preliminary treatment with roller electrodes, which are disposed in direct contact with the synthetic foil. In this preliminary treatment, a guiding roller is provided which forms one electrical pole, whereas a number of roller electrodes, which form the other electrical pole are applied to the other side of synthetic foil whilst it rotates around the guiding roller. An electrical-spark discharge (corona discharge) then takes place between the roller electrodes and the guiding roller, which produces the desired increase in the surface activity. However, only electrically non-conductive carrier strips are treated by this other known process.

The aim exists to simplify the device for implementing the process of the kind mentioned in the introduction, and to improve thedegree of efficiency of this process.

According to the present invention there is provided a method of improving the surface activity of electrically conductive carrier strips, wherein the surface of the strip is subjected to a high frequency and high gradient alternating electrical field formed between two electrodes, and wherein the carrier strip which forms one electrode is conducted over and in direct contact with a roller electrode which forms the other electrode and the surface of which comprises a solid dielectric material.

In accordance with the invention there is no interval i.e. no air gap between the roller electrode and the conductive carrier strip forming the other pole. No short circuits occur due to the presence of the dielectric and a uniform electrical discharge with a good appearance of sparks is obtained. The degree of efficiency is generally improved and, in particular, the device is of a particularly simple construction as only one single roller is necessary for the basic process and this roller acts at the same time as electrode and as guidingor transport roller. The carrier strip to be treated is simply placed over the roller electrode, and therefore few difficulties occur in the locating of the strip in the apparatus. It is no longer necessary to adjust the air gap, as said gap no longer exists. Further, it is of advantage that the treated conductive carrier strip can assist in removing the heat produced in the roller electrode as a result of its direct contact with the roller electrode. This is not possible in the case of the presence of an air gap. The heating of the treated carrier strip thereby produced, also causes the vaporization of water and oil remnants. Therefore, the drying for example of printing inks, is assisted and no cold shock occurs in extruder coating the strip with synthetic plastics material.

Thus the process in accordance with the invention does not only operate with a substantially more simple device, but also produces an even better result.

With the process in accordance with the invention, the carrier strip to be treated may not only be treated on one of its two sides, but a process may be used in which the carrier strip is passed over and in direct contact with at least two of said roller electrodes rotating in opposite directions, in such manner that one of its surfaces contacts one roller and the other of its surfaces contacts the other roller.

In order to increase the speed or degree of treatment, it is naturally possible to use more than one roller electrode to treat one surface of a carrier strip.

In accordance with the invention, the'improvement or increase of the surface activity, which is also called electrical bonding improvement, takes place as a result of various processes, which co-operate with one another to a greater or lesser degree, due to the effect of the high frequency alternating field namely, ion bombardment, electrode bombardment and corona discharge (spaced discharge). In the case of aluminum foils it is assumed that the increase in the surface activity can be mainly traced back to the ion bombardment in co-operation with the electron bombardment. The high frequency alternating field also frees the foil of surface water and other impurities. Thus an electrical spark discharge takes place through the solid dielectric material, and, in fact, between the electrically conductive carrier strip, which forms one pole, and the roller electrode, which forms the other pole. Conveniently the carrier strip is earthed whereas the high frequency alternating field is applied to the roller electrode by means of an appropriate generator.

The present invention will now be described by way of example and with reference to the drawing, which is; a diagrammatic side view of an apparatus for carrying out the method in accordance with the invention.

The terms top and bottom as used herein refer to relative positions as shown in the drawing.

For the case when the carrier strip is to be treated on its underside only, the strip is given reference 4, and is conducted over the top over at least one of the roller electrodes 1 or 2. For the case when the opposite surface alone is to be treated, the carrier strip is given the reference 5, is shown in broken line, and is conducted over the bottom of at least one of the roller electrodes. For the case when both surfaces are to be treated, the carrier strip, is given the reference 6, is shown in dashdotted line, and is conducted over at least two roller electrodes 1 and 2 in such manner that these rollers rotate in opposite directions. At least two roller electrodes are required in this last-mentioned method.

If a particularly high speed of operation is required or a more intensive preliminary treatment is to be effected, a correspondingly greater number of roller electrodes must be used.

The process in accordance with the invention is suitable for increasing the surface activity of the many different electrically conductive carrier strips. For example, the process may be used on conductive foils of metal, in particular of aluminum, compound foils consisting of non-metals and metals, or conductive paper, such as paper mixed with carbon.

The rollers are provided with a solid coating 3, having a relatively high dielectric constant. For use as a dielectric, many different types of synthetic plastics materials may be used, such as epoxy resins, and polyester compounds, and also glass may be used.

What 1 claims as my invention and desire to secure by Letters Patent of the United States is:

1. A method of improving the surface activity of electrically conductive carrier strips, wherein the surface of the strip is subjected to a high frequency and high gradient alternating electrical field formed between two electrodes, establishing the conductive carrier strip as one of said electrodes, establishing a roller as the other of said electrodes and wherein the peripheral surface of the roller comprises a solid dielectric material, and causing the conductive electrode strip to be conveyed toward and into direct contact with the dielectric surface of the electrode roller as the roller is revolved.

2. A method as claimed in claim 1, wherein the carrier strip is passed over and in direct contact with at least two of said electrode rollers rotating in opposite directions, in such manner that one of its surfaces contacts one roller and the other of its surfaces contacts the other roller.

3. A method as claimed in claim 1, wherein the strip is passed over and in contact with a plurality of rollers rotating in the same direction in such manner that only one of its surfaces contacts the rollers.

4. A method as claimed in claim 2, wherein the strip is passed over more than two rollers rotating alternately in opposite directions in such manner that adjacent rollers contact opposite sides of the strip.

5. A method as claimed in claim 1, wherein the strip is aluminum. 

2. A method as claimed in claim 1, wherein the carrier strip is passed over and in direct contact with at least two of said electrode rollers rotating in opposite directions, in such manner that one of its surfaces contacts one roller and the other of its surfaces contacts the other roller.
 3. A method as claimed in claim 1, wherein the strip is passed over and in contact with a plurality of rollers rotating in the same direction in such manner that only one of its surfaces contacts the rollers.
 4. A method as claimed in claim 2, wherein the strip is passed over more than two rollers rotating alternately in opposite directions in such manner that adjacent rollers contact opposite sides of the strip.
 5. A method as claimed in claim 1, wherein the strip is aluminum. 